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Update on SPICE Electric Circuit Simulations

Discussion in 'CAD' started by Ir. Hj. Othman bin Hj. Ahmad, May 11, 2007.

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  1. http://www.brorson.com/gEDA/SPICE/x496.html

    I was evaluating a few free and demo SPICE programs.

    I'm surprised that my port of SPICE 2G6 could be the most reliable
    Electric Simulator for large circuits. I did the port in 1990.

    I am surprised that many textbooks don't emphasise SPICE simulations
    in analysing circuits. I abandoned books that don't touch on this
    program.

    I believe it is vital for students who are exposed to electric
    circuits to learn how to handle and program SPICE. It is no longer
    necessary to calculate manually. You may know the priciples, but if
    you don't know how to calculate reliably how complex circuits behave,
    it is pointless to employers.

    I shall choose ORCAD Lite for most of my important simulations. It may
    be limited to a few components but it is sufficient for the course
    that I'm teaching. PSPICE is reasonably close to SPICE.

    I'm surprised the LTSPICE is not compatible. I tried the simplest
    SPICE circuit, but it didn't even recognise the .AC command.

    Tina from TI is also good but it insists on having an IC first.

    As a backup, TopSpice is a good choice. It may limit the number of
    components but it is small and run on PCs with Windows XP.

    http://penzar.com/topspice/topspice.htm

    I choose these programs based on their acceptance of standard SPICE
    source codes, that are called netlists by these CAD programs.

    For schematics, ORCAD is the best but too complicated. I had used them
    for design up to PCB layout but not its simulation functions. At that
    time, it was not convenient to program PSPICE for digital simulation.

    Despite the increase in speed of PCs, I still believe that digital
    simulations are based done by programs that are specialised for
    digital. I shall be evaluating VHDL compilers for a logic design
    course.

    Another advantage of working with SPICE is the large number of example
    circuits that SPICE can accept. Even commercial CAD programs have
    options to output into SPICE standard netlists that can be fed to
    SPICE programs.

    I notice that the current developments are in integrating schematic
    capture to simulation and plotting.

    The trouble is there are too many bugs. I had to refer to the
    traditional text output in order to get some information out of the
    simulations.

    LTSPICE somehow filter these outputs making it less informative.
    Topspice gives out all these intermediate files.

    Another advantage is the large amount of documentations of SPICE and
    its derivatives. I just got a large manual of all the dialects of
    SPICE.

    If you want to simulate a large number of components reliably, you
    may turn to my old dspice from simtel archives. It should be able to
    run on Windows XP on the command prompt either command.com or cmd.

    the output will be in text format so you'll need to adapt them to a
    good plotter, such as PROBE from PSPICE.

    After more than 15 years, the lack of reliable unlimitedly free SPICE
    simulators and its associated support programs is not encouraging.
    Worse, educators still don't want to expose students to SPICE,
    especially in Malaysia.

    Even in US, most textbooks ignore SPICE.

    It is as though, educators teach students how to count while ignoring
    completely calculators or tables.

    If we want to concentrate on priciples, the most important is just
    understanding Kirchoff's laws.

    All other techniques are just ways of analying manually which should
    be obsolete.
     
  2. Jim Thompson

    Jim Thompson Guest

    On 10 May 2007 19:26:26 -0700, "Ir. Hj. Othman bin Hj. Ahmad"

    [snip]

    Whatsamatta... did your virgin get away ?:)

    ...Jim Thompson
     
  3. Hello,

    I wonder what you did. LTspice is one of the most compatible SPICE
    programs on a netlist level.

    Many universities have switched to LTspice.
    The main reason is that LTspice is a free, fast, and unlimited SPICE
    simulator.
    This allows any student to simulate even the most complex circuit.
    http://www.linear.com/designtools/software/switchercad.jsp

    Are you aware that maybe 100000 people had managed to use
    LTspice for their SPICE simulations?

    LTspice recognises the ".AC" comamnd line of course.
    Please send me your LTspice schematic(.asc) and/or your
    LTspice netlist and I will tell you what you did wrong.

    Best regards,
    Helmut
    Moderator of the LTspice Yahoo group
    http://tech.groups.yahoo.com/group/LTspice/

    TINA-TI has another limitation too.
    It doesn't have E, F, G amd H sources in their schematic entry.
     
  4. Joel Kolstad

    Joel Kolstad Guest

    I'd think you'd be using 3F5? I'd be hard-pressed to still find a FOTRAN or
    RATFOR compiler these days. :)
    This isn't really true. Sedra & Smith, which is the textbook I used in
    college, had plenty of SPICE stuff in it back in the early '90s and the
    current version has even more.
    I suppose so, but most people coming out of college today are neither expert
    circuit designers nor expert SPICE modelers -- and becoming a really good
    SPICE user is generally far less demanding than becoming a really good
    designer.
    LTSPICE is quite compatible -- it sounds as though you didn't peruse its
    instruction manual?
    How so? My experience is that ORCAD *Capture* is quite simple to use, and I
    *wish* it had more sophisticated features (and fewer bugs).
    Yes. If you'd doing mixed analog/digital simulations, there's XSPICE or
    VHDL-AMS or Verilog-A -- what you end up using is often driven by what models
    are available.
    If you're going to be shipping any of your designers over here to the U.S.,
    Verilog is quite popular as well.
    Mmmm... it's been ongoing deveopment for some decades now...
    With what tool? Some are a lot buggier than others...
    I think one can make a pretty strong argument that the old text editor/command
    line SPICE/post-processor graphing utility approach to circuit design is -- in
    *most* cases -- not as effficient as the contemporary schematic
    capture/simulation/plotting "all in one" tools most people now use.
    Feel free to start patching the source code yourself? :) I mean, your
    statement is really too negative -- there are plenty of reliable, reasonably
    unlimited SPICEs that are used for real designs every day. It's true that if
    you're looking to do a modern IC design, yeah, good luck finding a 100% free
    design flow from SPICE to layout/DRC, but it's not like anyone's going to fab
    your design for free anyway, you know? There are universities that have older
    (donated) fab equipment and do have students design complete ICs along the
    lines of op-amps, logic gates, small ADCs/DACs, PLLs, etc., and this is quite
    valuable. The more common (it would seem) approach of universities using
    commercial software that's provided for free or heavily subsidized and using
    services such as MOSIS to do the IC run seems to work fine too: Thousands of
    new students make ICs every year, after all.
    Not true. I don't think you'd find a major US university today where students
    don't use SPICE in a EE curriculum.
    That's a start, but you're never going to be able to design decent op-amps if
    you haven't gone through a fair amount of analyzing circuit performance using
    loop analysis, phasor or Laplace domain techniques, etc. If you only know
    Kirchoff's laws and have a SPICE simulator, I just can't you ever suddenly
    coming up with, e.g., a Gilbert cell mixer or a Doherty power amplifier or
    even many of the fancier current sources out there.

    ---Joel
     
  5. qrk

    qrk Guest

    I think it's much more important to learn the basics. These days,
    there's a lot of information to take in during a 4 year period
    university term. This time is better spent learning basics. It's
    surprising how many engineers, coming out of the university, have a
    poor grasp of utilizing Ohm's Law when analyzing practical circuits.
    Spice is a valuable tool, but without a good grasp of the basics,
    Spice can produce misleading results. If the practitioner can't do the
    necessary paper or mental calculations to verify Spice results, this
    person is not valuable to employers.

    Many universities teach Spice basics, as evidenced by the number of
    Spice tutorials on the web from universities. To become proficient in
    Spice requires time, not necessarily in learning Spice, but becoming
    proficient in dealing with the analysis of semiconductor devices. The
    4 year university curriculum does not allow for this level of
    expertise and/or students learn enough to pass the test without
    understanding practical applications of what they learned.
    LTspice is very compatible with standard Spice syntax. I feed LTspice
    ASCII decks without problem from our filter programs and from PSpice
    decks. Yes, LTspice is nearly 100% PSpice syntax compatible. Post your
    deck and I'm sure someone can show you what your problem is. The other
    responders to your post are all proficient in Spice.
     
  6. Marra

    Marra Guest

    I wouldnt touch spice with a barge pole !

    If you add in stray capacitance, inductance, enclosure, spread of
    components then SPICE simply is useless.
     
  7. Jim Thompson

    Jim Thompson Guest

    I believe it is YOU who is useless ;-)

    ...Jim Thompson
     
  8. Some that don't:
    Allen and Holberg -- isbn: 0195116445
    Jakob Baker -- http://cmosedu.com
    But you need to know what buttons to push in which sequence. Did you
    walk right out of your mother?
    Kirchoff is tought in all junior electric classes. Then abandoned
    because there is SPICE. But it is still expected that the student know
    how Kirchoff works. When did you study? in the 60's? Did you study?

    In your analysis, I think you forgot to mention gnucap
    (www.gnucap.org) If you have capabilities in computer simulators, I
    think you should subscribe to the mailinglists mentioned there, or go
    to the gEDA pages at geda.seul.org and subscribe. You can do a lot
    more good to electronic engineering if contributing to free and open
    source than to post comparisons like the one you did here.
     
  9. Ahmmmm.......you are obviously a little unfamiliar with the capabilities of
    spice, and how 10,000's of analogue designers actually use spice to design
    in the pure virtual world, 10,000 transistor analogue circuits that work
    right first time. Modern analogue ic design is quite impossible without
    spice. No one in the i.c. world designs with real components. This is a
    fact.

    It is a little naive to suggest that modern design tools do not deal with
    aspects such as component variations and parasitic effects. Professional
    spice tools have many completely standard features to deal with such issues.
    To wit, Worst Case Corner model and Monty Carlo analysis, and parasitic
    extraction. Today, the models themselves are usually amazingly accurate.

    So, if it costs $100k for a mask set, just how do you imagine you are going
    to experiment with the real thing in order to produce a design?
     
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